Add CHANGELOG entry for kube-prometheus-stack version bump

Refs: #3279

CHANGELOG.md

@@ -28,6 +28,18 @@
   dex image from v2.27.0 to v2.28.1
   (PR[#3370](https://github.com/scality/metalk8s/pull/3370))
 
+- [#3279](https://github.com/scality/metalk8s/issues/3279) - Bump
+  kube-prometheus-stack charts version from 12.2.3 to 15.4.4.
+  The following images have also been bumped accordingly:
+   - grafana from 7.3.5 to 7.5.5
+   - k8s-sidecar from 1.1.0 to 1.10.7
+   - kube-state-metrics from v1.9.7 to v1.9.8
+   - node-exporter from v1.0.1 to v1.1.2
+   - prometheus from v2.22.1 to v2.26.0
+   - prometheus-config-reloader fomr v0.43.2 to v0.47.0
+   - prometheus-operator from v0.43.2 to v0.47.0
+  (PR[#3360](https://github.com/scality/metalk8s/pull/3360))
+
 ### Breaking changes
 
 - [#2199](https://github.com/scality/metalk8s/issues/2199) - Prometheus label